Process for the preparation of alkyl nitrates



Dec. 22, 1970 G. a. BACHMAN ET AL 3,549,687

PROCESS FOR THE PREPARATION OF ALKYL NITRATES Filed July 29, 1968 V WATER OUT WATER OUT 6." /ALKYL NITRATE LAYER MAGNETIC STIRRER INVENTORS GUSTAVE B. BACHMAN NEIL W CONNON United States Patent 3,549,687 PROCESS FOR THE PREPARATION OF ALKYL NITRATES Gustave B. Bachman, Lafayette, Ind., and Neil W. Connon, Rochester, N.Y., assignors to Purdue Research Foundation, Lafayette, Ind., a corporation of Indiana Filed July 29, 1968, Ser. No. 748,339 Int. Cl. C07c 77/02 US. Cl. 260-467 12 Claims ABSTRACT OF THE DISCLOSURE A process for preparing alkyl nitrates by contacting an alcohol, such as octyl alcohol, in liquid form with gaseous dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid and rapidly removing the alkyl nitrate from the reaction mixture.

SUMMARY OF THE INVENTION This invention relates to a process for the preparation of alkyl nitrates by contacting an alcohol in liquid form with gaseous dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid and rapidly removing the alkyl nitrate from the reaction mixture, In a particular aspect, the present invention relates to a process for the preparation of alkyl nitrates by contacting countercurrently a liquid stream of an alcohol with a gaseous stream of dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid and rapidly removing the alkyl nitrate from the reaction mixture.

It has long been known that alkyl nitrates are obtained by the reaction of alcohols with nitric acid or with mixtures of nitric acid and sulfuric acid. Representative references include US. Patent 2,254,352 to G. H. Cloud et al., US. Patent 2,734,910 to J. B. Hinkamp et al., US. Patent 2,618,650 to J. B. Hinkamp et al., and US, Patent 2,977,384 to R. Bentley et al. It is also known that alkyl nitrates are prepared by the reaction of an alcohol with dinitrogen tetroxide. Specifically, the preparation of butyl nitrate by the reaction of butyl alcohol and dinitrogen tetroxide in the presence of sodium butoxide at low temperatures is discussed in a paper by White and Feldman, Journal of American Chemical Society, 79, 832.

Each of the methods referred to possesses the serious drawback that a substantial portion of the alcohol starting material is consumed in the production of unwanted byproducts, in particular carboxylic acids. The production of the unwanted by-products is due principally to prolonged contact of the alkyl nitrate with nitric acid used in or produced by the process. This not only results in the reduction in yields of the alkyl nitrate but presents serious safety problems because of the explosive nature of mixtures of alkyl nitrates with nitric acid and other reaction products. These methods also present recovery problems due to the necessity to separate the alkyl nitrate from other reaction products. Further, the dinitrogen tetroxide reaction procedure requires very low temperatures, on the order of 75 C., thereby necessitating the employment of elaborate cooling equipment.

It is an object of the present invention to provide a process for the preparation of alkyl nitrates.

It is a further object of the present invention to provide a process for the preparation of alkyl nitrates from alcohols wherein the production of unwanted by-products is minimized.

It is a still further object of the present invention to provide a process for the preparation of alkyl nitrates whereby the hazards inherent in prior art processes are minimized.

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It is an additional object of the present invention to provide a process for the preparation of alkyl nitrates without the employment of extremely low temperatures, that is, temperatures on the order of about C.

Other objects and advantages of the present invention {Ill be apparent from the specification and appended c aims.

It has been discovered in accordance with the present invention that alkyl nitrates are obtained without the previously discussed drawbacks of prior art processes by contacting an alcohol in liquid form with gaseous dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid and subsequently rapidly removing the thus formed alkyl nitrate from the reaction mixture. The following equation illustrates the reaction. In the equation R represents an alkyl radical.

ROH+N O RONO +HNO DETAILED DESCRIPTION In carrying out the process of the present invention, the alcohol and the dinitrogen pentoxide are contacted under reaction conditions to form a reaction mixture containing alkyl nitrate and nitric acid and the alkyl nitrate is rapidly removed from the reaction mixture. The process is preferably conducted by countercurrently contacting a liquid stream of aliphatic alcohol and a gaseous stream of dinitrogen pentoxide in a continuous manner.

In a specific embodiment of the present invention, a liquid alcohol, such as octyl alcohol, is converted into the nitrate by contact with gaseous dinitrogen pentoxide in an apparatus as illustrated in the single figure.

Referring to the figure, anhydrous liquid octyl alcohol is continuously fed into a vertical, spiral reaction column 1 and passes downward and through the column. Simultaneously, gaseous dinitrogen pentoxide is continuously fed into the reaction column and passes upward and into contact with the descending alcohol. Throughout the reaction, the reaction column and its contents are cooled by a jacket of cooling water 2. The resultant reaction mixture containing octyl nitrate and nitric acid flows downward through a tube 3 into a quenching vessel 4 where it is mixed with water. The water serves both as an extractant and as a quenching agent, thereby minimizing the possibility of react-ion between the alkyl nitrate and nitric acid and any other reaction products formed before and during separation of the alkyl nitrate from the reaction mixture. As the process proceeds, a liquid mixture of water and reaction mixture is continuously drawn ofi through a line 5 to a separation vessel 6. Throughout the process, additional water is continuously passed into the quenching vessel. The liquid mixture is the separation vessel separates on standing into an upper octyl nitrate layer and a lower aqueous layer. Continuous removal of the octyl nitrate layer from the aqueous layer is accomplished by drawing the octyl nitrate otf through a line 7 to a collection vessel, not shown. The aqueous layer is continuously removed through a line 8. v

The reaction vessel employed in the process of the present invention together with most of the associated lines and equipment is preferably made of or lined with acid-resistant materials owing to the generally corrosive nature of the products under the conditions employed. Glass is especialy well suited for this purpose because of its excellent resistance to corrosive materials.

It is to be distinctly understood that the process of the present invention is not limited to the type of apparatus described herein but may be carried out in any type of apparatus which would be recognized as suitable by those, skilled in the art.

The nitration reaction may be conducted over a wide temperature range, with a temperature in the range of from about 70 to about +40 C. being typically employed. Temperatures below about 70 C. are generally not practical because of the slow rate of reaction, while temperatures above +40 C. tend to cause substantial decomposition of reactants and the reaction products, in particular the dinitrogen pentoxide. A temperature in the range of from about to about +30 C. is preferred.

The molar ratio of dinitrogen pentoxide to alcohol may also be varied over a wide range, with a ratio of dinitrogen pentoxide to alcohol in the range of from about 1.511 to about 1:1 being generally preferred. A molar ratio of dinitrogen pentoxide to alcohol in the range of from about 1.2: l to about 1.1 :1 is especially preferred.

Any suitable alcohol may be employed in the process of the present invention. Typically employed alcohols are those monohydroxy and dihydroxy alcohols having from 1 up to about 20 carbon atoms, as for example, ethyl accompanying drawing. It is understood that the examples are presented for the purpose of illustration only and are not intended as a limitation of the invention.

Example 1 The reaction was carried out at a temperature of approximately C. The conversion to octyl nitrate was 95% based on octyl alcohol.

Examples 2-5 Additional examples of the preparation of alkyl nitrates are given in the following table.

TAB LE I Addition rate of reactants (moles per hour) (onvcrsiun Tcinpvr- Reaction percent Dinitrogen aturc tinio Solvent for based on Alcohol Alcohol pentoxide t C (hours) alcohol alcohol Example No.2

" Dccyl alcohol..." 0.084 0.0516 20 7. 75 None .02 (yclohexyl alcohol O. 080 0. 096 20 6. 75 Nitroniethaiic Ht lropyl alcohol v v 0. 000 0.1020 20 5.0 do l .It 5 2-0ctyl alcohol. 0. 002 U. 1000 '20 3. 5 Nitroothanah. 00

alcohol, tertiary butyl alcohol, cyclohexyl alcohol, cyclo- 3 Example 6 pentyl alcohol, 1,5-pentanediol, secondary butyl alcohol, 1,6-hexanediol, octyl alcohol, propyl alcohol, decyl alcohol, 2-chloroethyl alcohol, heptyl alcohol, dodecyl alcohol, isopropyl alcohol, 3-methyl-3-hydroxy-pentane, t-amyl alcohol, and the like. Because of the tendency of tertiary alkyl nitrates to hydrolyze rapidly in water, it is preferred when employing a tertiary alcohol as the starting material to avoid contacting the reaction mixture with water. Accordingly, when a tertiary alcohol is employed, the reaction mixture is preferably added to a suitable non-aqueous, inert solvent for the nitrate and the nitrate is then recovered from solution, as for example, by distillation. Examples of suitable solvents include the aliphatic hydrocarbons, such as pentane, heptane, hexane, and the like. The solvent preferably contains a complexing agent for nitric acid which will not react with the alkyl nitrate, such as, for example, sodium fluoride.

The aliphatic alcohol employed should be substantially free of other substances which react with dinitrogen pentoxide. An example of such a substance is water which. as is well known, forms nitric acid in reaction with dinitrogen pentoxide. Accordingly, it is preferred to employ substantially anhydrous aliphatic alcohols.

As previously indicated, the alcohol is employed in liquid form. When it is desired to operate the process at a temperature below the freezing point of the particular alcohol of choice, a suitable inert solvent for the alcohol which is liquid at the temperature employed may be used. Examples of such solvents include chloroform, carbon tetrachloride, and the lower nitroalkanes, for example, nitromethane, nitroethane, and nitropropane.

The dinitrogen pentoxide of use in the present invention may be prepared by any suitable procedure, such as, for example, by the reaction of N0 with ozone in the known manner.

The invention will be understood more fully by reference to the following specific examples. The examples illustrate the application of the present invention to a variety of alcohols. In each case the procedure followed was essentially that set forth in the description of the Essentially the same procedure used in Example 1 was employed except that 1,5-pentanediol was substituted for octyl alcohol and a mixture of nitromethane and dimethyl sulfoxide was used as a solvent. Pentamethylene dinitrate was obtained in a conversion of 83%.

Example 7 Essentially the same procedure used in Example 1 was employed except that 2-chloroethyl alcohol was substituted for octyl alcohol and nitromethane was used as a solvent. 2-chloroethyl nitrate was obtained in a conversion of Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing is to be interpreted as illustrative only and the invention is defined by the claims appended hereto.

We claim:

1. A process for the preparation of alkyl nitrates which comprises contacting an alcohol in liquid form with gaseous dinitrogen pentoxide, thereby forming a reaction mixture containing alkyl nitrate and nitric acid and rapidly removing the said alkyl nitrate from the reaction mixture.

2. The process of claim 1 wherein the temperature is above about -70 C. but below temperatures causing substantial decomposition of the nitrate, the alcohol or the dinitrogen pentoxide.

3. The process of claim 1 wherein the alcohol and the dinitrogen pentoxide are contacted countercurrently.

4. The process of claim 3 carried out in a continuous manner.

5. The process of claim 3 wherein the alcohol comprises a liquid stream and the dinitrogen pentoxide comprises a gaseotts stream.

6. The process of claim 2 wherein the temperature is in the range of from about 0 to about 30 C.

7. The process of claim 1 wherein the molar ratio of dinitrogen pentoxide to alcohol is in the range of from about L5: 10 to about l.l 1.0.

8. The process of claim 7 wherein the molar ratio of dinitrogen pentoxide to alcohol is in the range of from about 1.2:1.0 to about 1.1:1.0.

9. The process of claim 1 wherein the alcohol is a monohydroxy or a dihydroxy alcohol containing from 1 to about 20 carbon atoms.

10. The process of claim 9 wherein the said alcohol is a primary or a secondary alcohol.

11. The process of claim 10 wherein the said alkyl nitrate is removed from the said reaction mixture by adding the reaction mixture to water, permitting the resulting mixture to separate into an alkyl nitrate layer and an aqueous layer and removing the alkyl nitrate layer from the aqueous layer.

References Cited UNITED STATES PATENTS 3,409,620 11/1968 Ohman et a1. 260467 OTHER REFERENCES Boschan et a1.: Chem. Reviews, vol. 55, pp. 485 to 488 (1955).

Rodds Chemistry of Carbon Compounds, S. Coffey, editor, 2nd ed., vol. I, Part B, Elsevier Pub. Co., London,

10 1964, pp. 57 to 60.

LELAND A. SEBASTIAN, Primary Examiner US. Cl. X.R.

'12. The process of claim 9 wherein the alcohol is a 15 045 tertiary alcohol.

UNITED STATES PAIICNT 0mm:

CERTIFICATE OF CORRhCTION Patent No. U.S. 3,5'+9 6 87 Dated December 22 1970 Inventor) Gustave B. Bachman and Neil W. Connon It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 65 "especialy" should be -especially--.

Column 4 line 75 claim 7 "1.5 :10" should be --l.5 :l.O--.

Signed and sealed this 6th dhy of April 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SGHUYLER, J Attesting Officer Commissioner of Patent 

